1. Field of the Invention
The present invention relates to a heat sensitive flow meter and a fuel controller using the same.
2. Related Background Art
In general, in a heat sensitive flow meter for measuring a flow rate of a fluid such as intake air of an internal combustion engine of an automobile or the like, it is known that a magnitude of an output signal of the flow meter does not show a proportional relationship (linear model) to the flow rate, but shows a non-linear relationship in which a rate of increase in the magnitude of the output signal of the flow meter is more slowly changed as the flow rate is further increased. At this time, it is known that in a case where in the heat sensitive flow meter, a response of the flow meter is delayed due to an influence of a large heat capacity of a flow rate detection unit, or an influence of a low-pass filter (hereinafter referred to as “LPF” for short) installed in an interface between the flow meter and a fuel controller, when an intake gas pulsation of an engine is generated, a mean flow rate calculated by the flow meter become less than an actual mean flow rate in cooperation with the above-mentioned non-linearlity of the output signal to the flow rate calculated from the flow meter.
For this reason, there is proposed a technique providing a delay means for, when a signal obtained from a flow rate detection unit is delayed, delaying an output signal in a direction of a decrease of a flow rate after discriminating the direction of decrease from the direction of increase of a flow rate (refer to JP 62-36522 B for example).
In JP 62-36522 B, an increase and a decrease in flow velocity are discriminated with a diode, causing a response to be more lagged when the flow velocity is decreased than when the flow velocity is increased.
That is to say, in one embodiment described in JP 62-36522 B, there is adopted a configuration that when a flow velocity is increased, a signal is transmitted without delaying a response, while when a flow velocity is decreased, a response is delayed on the basis of a time constant determined by a capacity of a capacitor and a resistance value of a resistor.
In addition, in another embodiment described in JP 62-36522, a signal transmission path when a flow velocity is increased and a signal transmission path when a flow velocity is decreased are changed over to each other in order to change a resistance constant thereby changing a time constant.
Since in the technique disclosed in JP 62-36522 B, the response is caused to be more lagged when the flow velocity is decreased when the flow velocity is increased, for example, there is encountered a problem that sufficient effects can not be obtained in a pulsation signal on which higher harmonics are superimposed.